Device and method to control a power source

ABSTRACT

Apparatus, devices, and methods for providing a voltage reduction capability in a welding power source for safety purposes. The resistive load and the output voltage of the welding power source output are monitored and compared to predefined or preselected threshold values to generate a load condition signal and an output voltage condition signal (e.g., logic signals). The load condition signal and the output voltage condition signal serve as inputs to a voltage reduction device control logic which generates control signals to enable and disable the input and output of the welding power source according to the defined control logic. As a result, an extra measure of safety in preventing electrical shock is provided to users of the welding power source during hazardous operating conditions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of U.S.patent application Ser. No. 12/946,071 filed on November 15, which isincorporated herein by reference in its entirety. In addition, thedescription of the preferred embodiment section and the drawings of U.S.Pat. No. 7,238,917 issued on Jul. 3, 2007 are incorporated by referenceherein in their entirety.

TECHNICAL FIELD

Certain embodiments relate to welding power sources. More particularly,certain embodiments relate to devices and methods for providing avoltage reduction capability in welding power sources for safetypurposes.

BACKGROUND

Several techniques have been used to reduce the open circuit voltage ofan arc welding power source before the welder is to be used for awelding process. One of the most common designs is a control circuitthat reduces the conduction period of the output switching devices, sothe open circuit voltage is retained at a desired lower value. In aninverter type power source, the switching devices are usually in theform of field effect transistors (FETs) or insulated gate bi-polartransistors (IGBTs). Since the switching frequency is usually greaterthan 20 kHz, the conduction period of these switching devices is veryshort and depends upon the operating frequency of the inverter. In orderto reduce the open circuit voltage to a low level, the minimumconduction period of the switching devices requires a complicated andelectrically demanding control circuit. Power sources employing suchopen circuit voltage (OCV) control devices also include a circuit torelease the control of the power source to allow the welding power to beobtained during welding. Such detection devices with releasing circuitsare usually prone to noise and sensitivity problems.

Further limitations and disadvantages of conventional, traditional, andproposed approaches will become apparent to one of skill in the art,through comparison of such approaches with embodiments of the presentinvention as set forth in the remainder of the present application withreference to the drawings.

BRIEF SUMMARY

Embodiments of the present invention comprise devices and methods forproviding voltage reduction capability in welding power sources forsafety purposes. The resistive load and the output voltage of thewelding power source output are monitored and compared to predefined orpreselected threshold values to generate a load/no-load condition signaland a high/low output voltage condition signal (e.g., logic signals).The load/no-load condition signal and the high/low output voltagecondition signal serve as inputs to a voltage reduction device controllogic which generates control signals to enable and disable the inputand output of the welding power source according to the defined controllogic. As a result, an extra measure of safety in preventing electricalshock is provided to users of the welding power source in hazardousoperating conditions.

These and other features of the claimed invention, as well as details ofillustrated embodiments thereof, will be more fully understood from thefollowing description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic block diagram of an example embodiment ofan electric arc welding system which may incorporate a voltage reductioncapability for safety purposes, in accordance with various embodimentsof the present invention;

FIG. 2 is provided to illustrate a schematic block diagram of an exampleembodiment of a prior voltage reduction capability implemented in theprior electric arc welder embodiment (as described in the preferredembodiment section and drawings of U.S. Pat. No. 7,238,917 which areincorporated herein by reference) which may also be implemented in theelectric arc welding system 900 of FIG. 1;

FIG. 3 illustrates a schematic block diagram of an example embodiment ofan improved voltage reduction device implemented in a first embodimentof a welding power source that may be implemented in the electric arcwelding system of FIG. 1;

FIG. 4 illustrates a schematic block diagram of an example embodiment ofan improved voltage reduction device implemented in a second embodimentof a power source of the electric arc welding system of FIG. 1;

FIG. 5 illustrates a schematic block diagram of an example embodiment ofan improved voltage reduction device implemented in a generic embodimentof a power source of the electric arc welding system of FIG. 1;

FIG. 6 illustrates a schematic diagram of an example embodiment of avoltage reduction device (VRD) control logic and associated logic truthtable implemented in the voltage reduction devices of FIGS. 3-5; and

FIG. 7 is a flowchart of an example embodiment of a method for providingvoltage reduction capability in the electric arc welder of FIG. 1 usingthe voltage reduction devices of FIGS. 3-5 and the voltage reductioncontrol logic of FIG. 6.

DETAILED DESCRIPTION

FIG. 1 illustrates a schematic block diagram of an example embodiment ofan electric arc welding system 900 which may incorporate a voltagereduction capability for safety purposes in accordance with variousembodiments of the present invention. The system 900 includes a powerconverter 910 providing welding output power between a welding electrodeE and a workpiece W. The power converter 910 may be of an inverter typethat includes an input power side and an output power side, for example,as delineated by the primary and secondary sides, respectively, of awelding transformer. Other types of power converters are possible aswell. A wire feeder 920 feeds the wire welding electrode E toward theworkpiece W. Alternatively, the electrode E may be a stick electrodeand, therefore, the wire feeder 920 is not used.

The system 900 further includes a waveform generator 930 and a weldingcontroller 940. The waveform generator 930 generates welding waveformsat the command of the welding controller 940. The waveform generated bythe waveform generator 930 modulates the output of the power converter910 to produce the welding output power between the electrode E and theworkpiece W.

The system 900 may further include a voltage feedback circuit 950 and acurrent feedback circuit 960 to monitor the welding output voltage andcurrent between the electrode E and the workpiece W and provide themonitored voltage and current back to the welding controller 940. Thefeedback voltage and current may be used by the welding controller 940to make decisions with respect to modifying the welding waveformgenerated by the waveform generator 930 and/or to make other decisionsthat affect safe operation of the system 900, for example.

U.S. Pat. No. 7,238,917 describes a prior electric arc welder embodimenthaving a voltage reduction capability for safety purposes. As a way tointroduce the detailed description of certain improved embodimentsdescribed herein, FIG. 2 is provided to illustrate a schematic blockdiagram of an example embodiment of a prior voltage reduction capabilityimplemented in the prior electric arc welder embodiment (as described inthe preferred embodiment section and drawings of U.S. Pat. No. 7,238,917which are incorporated herein by reference) which may also beimplemented in the electric arc welding system 900 of FIG. 1, forexample. The welder shown in FIG. 2 is of the type used for AC or DCwelding for MIG welding, TIG welding, stick welding and submerged arcwelding in both CC and CV modes.

The welder of FIG. 2 includes power source 10 having a three phase input12 and output terminals 14, 16 connected to welding cables 30, 32,respectively. The welding operation is schematically illustrated as anelectrode E, which can be a consumable wire directed toward workpiece WPconnected to ground terminal 34. Gap G is located between electrode Eand workpiece WP and is used in standard welding technology. The averagewelding current is measured by shunt 36. When welding is performed bythe welder, power source 10 is activated to provide power at terminals14, 16.

Power source 10 is preferably an inverter based power source having anON terminal 18 controlled by the logic on input line 20. A logic one orstarting signal on line 20 activates power source 10 to provide weldingpower at terminals 14, 16. A logic zero on line 20 (no starting signal)turns power source 10 off or down to a very low open circuit voltage.Power source 10, when activated, has an open circuit voltage acrossterminals 14, 16 which is high. When the power source is deactivated bya logic zero on line 20, the open circuit voltage of power source 10 iszero. To turn the power source fully on, switch 40 or a contact from thetrigger of the welding gun is closed in accordance with standardtechnology.

The welder of FIG. 2 relates to the concept of maintaining the powersource at zero open circuit voltage until switch 40 is closed and thereis a low resistance across gap G. This low resistance indicates that thewelder is in a condition preparatory to beginning the welding operation.A resistance across gap G greater than the set given amount indicatesthat the gap is still open and there is a demand for no open circuitvoltage or a low OCV. An open circuit voltage is not required or desiredin a welding operation until the welding process is to be initiated.This condition of the gap is recognized as a low resistance across gapG. Indeed, the resistance is often zero by electrode E touchingworkpiece WP to start the welding process. The open circuit voltage ofthe power source 10 is maintained at zero or a low level (which isequivalent to zero) until there is a detected indication that a weldingoperation is being initiated. This event is accomplished by determiningthe resistance across gap G.

A more specific use of the welder of FIG. 2 is creating “an enablesignal” when (a) the welding operation is initiated by a low resistancein gap G (creating a “start signal”) and (b) trigger switch 40 isclosed. The closing of switch 40 is a positive act after or when theelectrode approaches or contacts workpiece WP. Power source controldevice D is used to reduce the open circuit voltage of power source 10until the resistance in gap G is below a given amount, which givenamount is generally less than 100 ohms, 50 ohms, or 30 ohms according tothe desired setting of device D. Device D includes an input transformer60 having a primary winding 62 and a secondary winding 64. Winding 64 isa single turn of cable 30, which cable is passed through a tube. Aboutthe tube is a toroid with three turns wound upon it, which constitutesthe primary winding 62. The tube as defined above could be a conductorsuch as copper or aluminum so that cable 30 electronically terminates atboth ends of the tube. This is known transformer technology, where oneturn is a low resistance strap. Primary winding 62 is energized at ahigh frequency by a low voltage signal created by oscillator 70. The setfrequency is generally greater than 50 kHz and preferably in the rangeof 60 to 90 kHz. In practice, oscillator 70 is set at 85 kHz. Thecurrent of this signal is limited to a low value. In accordance with anembodiment of the present invention, the signal current is less than 40ma.

Input transformer 60 induces a high frequency low voltage signal intothe series circuit comprising cable 30, electrode E, gap G, workpieceWP, shunt 36, cable 32 and the internal resistance and inductancebetween terminals 14, 16 of power source 10. Consequently, a highfrequency signal is induced into this series circuit. The obtainablemagnitude of this signal is determined by the resistance in gap G. Thismagnitude is sensed by output transformer 80 having a primary winding 82and a secondary winding 84. Winding 82 is a single turn winding such assecondary winding 64 of input transformer 60. The high frequency signalinduced into secondary winding 84 is directed to the tuned decodingdetector 90 which detector is constructed in accordance with standardtechnology to provide a logic signal on output 92 when the resistance ofgap G is below a given amount. Consequently, a logic 1 on output startsignal line 92 indicates that electrode E is touching workpiece WPpreparatory to and beginning a welding operation. A “start signal” inline 92 is created when gap G has a resistance less than a given amount.To accomplish this objective, there is an input transformer inducing ahigh frequency low voltage signal in the series circuit including gap G.Output transformer 80 detects and measures the magnitude of the signalat the set frequency. The magnitude of any signal at the set highfrequency is measured by detector 90 and creates an output logic one or“start signal” on line 92. How this start signal is used to start powersource 10 is in accordance with another aspect of an embodiment of thepresent invention. The broad concept as described can be used withdiverse starting logic for power source 10.

In accordance with an embodiment of the present invention, power sourcecontrol device D utilizes a “start signal” on line 92. This signal isused to control power source 10. The “start signal” is one input of anANDing circuit 100 having a second input 102 from contact 40 a of thetrigger switch. The term contact or switch will be used interchangeablyfor items 40 and 40 a. Contacts 40 and 40 a are the trigger switchcontacts which are closed when a welding operation is initiated by anoperator or by an automatic mechanism. Device D may include only contact40 a. However, the other contact 40 is also illustrated to show thatpower source 10 is not operated until there is a low resistance at gap Gand the trigger is closed to initiate the welding operation. ANDingcircuit 100 has output 104 for an “enabling signal” that is a logic onewhen the power source 10 is to be fully on. This enable signal does notoccur unless the trigger switch 40 a is closed. Thus, contact 40 isclosed by means 40 b to connect line 20.

Output 104 of ANDing circuit 100 is directed to starting circuit 110 inthe form of an OR gate with one input being the “enabling signal” online 104. Thus, when line 104 is a logic one, output 112 of startingcircuit 110 is a logic one. This starts power source 10 so it is at fullpower, i.e. welding power. With switch 40 a closed, switch 40 is alsoclosed. In most welder power sources, there is an internal low impedancebranch between terminals 14, 16 as represented by the parallel circuitof capacitor 252 and resistor 254. If device D is retrofitted on a powersource without a low impedance between its output terminal, such circuitis added so the series circuit with gap G has a low impedance.

Switch 40 in line 20 can be eliminated in practicing various embodimentsof the present invention. However, it is used with an override networkinvolving a welding current detector. After a “start signal” in line 92,the welding cycle commences and welding current flows. As long as thereis welding current, the power source should stay at the full on state.The full on state means it has a welding power which may be low, such aswith TIG welding. When the welding current flows, transformers 60, 80may saturate and become ineffective to maintain a logic one on line 92.There is no “start signal” after the device D has accomplished itsobjective at the start of a welding cycle. To hold the power source onafter the transformers saturate, the logic network includes an overridesegment in the form of comparator 120. The voltage or input signal online 122 is provided by welding current averaging circuit 124.Consequently, the voltage on line 122 is representative of the averagewelding current of welder W. This average welding current is compared bydetector 120 with the voltage on a second input 126. This input has avoltage representing a low reference current x. By this logic network,when the average welding current represented by the voltage on line 122is greater than a certain fixed lower amount, (and the transformers aresaturated) comparator or welding current detector 120 produces a logicone on output line 130 which is a “welding current signal.”

The welding current signal on line 130 can be used in two separatebranches of device D. The first branch directs the welding currentsignal on line 130 to AND gate 140 having an input 142 represented by alogic one upon closing of trigger switch 40 a. This action releases gate140 for operation in accordance with the logic on input line 130. Thus,the logic on line 144 is a “welding current signal” appearing when thereis a welding current of at least a small amount. In this branch of thewelding current signal processor feature used in device D, the logic online 144 is enabled only when trigger switch contact 40 a is closed.

In an alternative, optional operation, as illustrated by dashed line150, the logic on line 144 merely reflects the logic on line 130. When alogic one appears on line 144 there is a welding current above a givensmall amount. When this occurs, starting circuit 110 is activated toproduce a starting signal or logic on line 112. In this optionaloperation, when there is a welding current and the trigger switch isclosed, switch 40 is closed and the power source is on. When the weldingoperation is stopped, trigger switch contact 40 is opened. Power source10 is deactivated to a zero open circuit voltage awaiting the nextstarting operation implemented and controlled through device D. As canbe seen, trigger switch 40 may be eliminated and is used primarily whenthe device D generates a welding current signal bypassing the remainderof the circuitry of device D. So whenever there is welding currentand/or the transformers are saturated, the power source is still heldon.

As can be appreciated from FIG. 2, device D turns on power source 10when the resistance across gap G is below a given amount, which isaccomplished by inducing a high frequency, low voltage signal in aseries circuit including the gap and measuring the magnitude of thesignal by a tuned detector (receiver) to create a start signal in line92. Otherwise, the power source remains off with a zero open circuitvoltage. It is possible to use transformers that do not saturate, thenthe start signal will be held during welding and there is no need forthe override portion of the logic network.

Again, the welder of FIG. 2 was previously disclosed in U.S. Pat. No.7,238,917. Improvements and modifications to the voltage reductiondevice capability of U.S. Pat. No. 7,238,917 will now be describedherein in accordance with FIGS. 3-7.

FIG. 3 illustrates a schematic block diagram of an example embodiment ofan improved voltage reduction device implemented in a first embodimentof a welding power source 300 that may be implemented in the electricarc welding system 900 of FIG. 1. FIG. 3 shows an input power side ofthe power source 300, being on the primary side of a welding transformer310, and an output power side of the power source, being on thesecondary side of the welding transformer 310.

The input power side of the power source 300 in FIG. 3 includes theprimary winding 311 of the single phase welding transformer 310 alongwith an input power contact relay CR having an energizing coil 321 and aset of electrical relay contacts 322. The primary winding 311 and therelay contacts 322 are in series with an input power source V_(IN) whenV_(IN) is applied to the input of the power source 300. The input powerside also includes an auxiliary transformer 330 having a primary sideconnected to V_(IN) and a secondary side connected to a main ON/OFFswitch 340 of the power source 300. The main ON/OFF switch 340 isaccessible to a user on the front panel of the power source 300, inaccordance with an embodiment of the present invention.

As can be seen in FIG. 3, the secondary side of the auxiliarytransformer 330 includes a secondary winding 332 in series with theON/OFF switch 340, the relay coil 321, and a voltage reduction device(VRD) switch 350. In order for the relay coil 321 to be energized by thesecondary winding 332 of the auxiliary transformer 330, both the ON/OFFswitch 340 and the VRD switch 350 must be closed. When the relay coil321 is energized, the contacts 322 of the contact relay CR are closedand current is able to flow from V_(IN) through the contacts 322,through the primary winding 311 of the welder transformer 310, and backto V_(IN) (and vice versa).

The power source 300 also includes a VRD power supply 360 which connectsto and derives power from the secondary side of the auxiliarytransformer 330 on the input power side of the power source 300, asshown. The VRD power supply 360 is part of the VRD device and provideselectrical power to the various VRD components in the power source 300as needed. The various VRD components that power may be supplied to invarious embodiments may include the VRD switch 350, a VRD control logic370, an oscillator circuit 380, and a tuned receiver circuit 390, theoperation of which are described in more detail later herein. Inaccordance with an embodiment of the present invention, all of the VRDcomponents are located internally within the power source 300, making itdifficult for a user to override the VRD functionality described herein.

As current flows through the primary winding 311 when the contacts 322of the contact relay CR are closed, the secondary winding 312 of thewelding transformer 310 may be energized on the secondary side of thepower source 300. The secondary side of the power source 300 may includeone or more output control power switching devices such as siliconcontrolled rectifiers (SCR's), IGBT's, or FET's, for example, as arewell known in the art. As an example, FIG. 3 shows an SCR 395 connectedto the secondary winding 312 of the welding transformer 310. The SCR 395is shown generically and may represent a plurality of SCR's in an outputconfiguration. The oscillator circuit 380 is connected to the output ofthe SCR 395 as shown on the electrode side E of the output current pathof the power source 300. The tuned receiver circuit 390 is connected tothe secondary winding 312 on the workpiece side W of the output currentpath of the power source 300. However, other configurations are possibleas well, in accordance with other embodiments of the present invention.For example, the oscillator circuit 380 may instead be on the workpieceside W and the tuned receiver circuit 390 may be on the electrode sideE. Furthermore, both the oscillator circuit 380 and the tuned receivercircuit 390 may be implemented in series on either the electrode side Eor on the workpiece side W, for example.

The output side of the power source 300 also includes a voltage feedbackcircuit 375 and a current feedback circuit 376 providing signals beingrepresentative of output voltage and output current to the input of theVRD control logic 370. The output voltage may be sampled across thewelding output terminals A and B of the power source 300, and the outputcurrent may be sampled through a shunt device 396 in the welding outputcurrent path. In accordance with various embodiments of the presentinvention, the voltage feedback circuit 375 may provide a signal 373,which may be a RMS voltage signal or a logical (high/low) output voltagecondition signal for example, to the VRD control logic 370. Furthermore,in accordance with various embodiments of the present invention, thecurrent feedback circuit 376 may provide a signal 374, which may be anaverage current of the welding output to the VRD control logic 370 or alogical (high/low) output current condition signal for example, to theVRD control logic 370. Other types of signals being representative ofthe output voltage and the output current are possible as well.

The output side of the power source 300 further includes an outputcontroller 399 and the VRD control logic 370. Just as the voltagefeedback circuit 375 and the current feedback circuit 376 providesignals to the VRD control logic 370, the tuned receiver circuit 390provides a signal 376 to the VRD control logic 370 which may be aresistance level signal or a logical (high/low) load/no-load conditionsignal. The signal 376 provided by the tuned receiver circuit 390defines a load condition or a no-load condition at the output of thewelding power source 300. A load condition corresponds to a relativelylow resistance between the electrode E and the workpiece W (e.g., whenwelding), whereas a no-load condition corresponds to a relatively highopen circuit resistance value between the electrode E and the workpieceW (e.g., when not welding).

The oscillator circuit 380 and the tuned receiver circuit 390 operate inmuch the same manner as the corresponding oscillator and decode detectorcircuit components of FIG. 2 herein. The oscillator circuit 380 inducesan oscillating signal (e.g., at 80 kHz) in the welding output currentpath and the tuned receiver circuit 390, which is tuned to the frequencyof the oscillating signal, receives the induced oscillating signal inthe welding output current path. Both the inducing and the receiving areaccomplished via transformer coupling to the welding output circuit pathwithin the power source 300. Such transformer coupling is described indetail in U.S. Pat. No. 7,238,917. The level of detection or sensing bythe tuned receiver circuit 390 depends on the load or resistance betweenthe electrode E and the workpiece W. The level of detection may becompared to a threshold value to define a load condition or a no-loadcondition of the welding output. A trigger switch signal 377 from, forexample, a welding gun may also serve as an input to the VRD controllogic 370, in accordance with an embodiment of the present invention.

The VRD control logic 370 operates on some or all of the input signalsto produce an output enable signal 371 that is provided to the outputcontroller 399. For example, in accordance with an embodiment of thepresent invention, the output controller 399 may disable the output sideof the power source 300 (e.g., by turning off the SCR 395) when theload/no-load signal 376 indicates a no-load condition. Similarly, theoutput controller 399 may enable the output side of the power source 300(e.g., by turning on the SCR 395) when the load/no-load signal 376indicates a load condition. In this manner, when the welder is notcurrently being used for welding but is connected to an input powersource V_(IN) and the on/off switch 340 is on, a higher resistance(no-load condition) is detected and the output of the power source 300is disabled.

Furthermore, the VRD control logic 370 operates on some or all of theinput signals to produce an input disable signal 372 that is provided tothe VRD switch 350 on the input power side of the power source 300. Forexample, in accordance with an embodiment of the present invention, theVRD switch 350 (which is normally closed) may be opened when theload/no-load condition signal 376 indicates a no-load condition and thehigh/low output voltage condition signal 373 indicates a high outputvoltage condition. In this manner, the contact relay 322 is opened whenthe VRD switch 350 is opened, disallowing current to flow through theprimary winding 311 of the welder transformer 310. Therefore, outputpower cannot be generated on the secondary or output side of the powersource 300.

In this manner, an extra measure of safety is provided. For example,even if the output of the power source 300 is being commanded to bedisabled by the output controller 399 because of a no-load conditionbeing detected, an output voltage could still appear across the outputterminals A and B if a failure or defect occurs in the output side ofthe power source 300. For example, if the SCR 395 were to fail byshorting, a relatively high output voltage level could still appearacross the terminals A and B, which can be potentially dangerous duringa non-welding (no-load) situation. However, the high output voltagecondition is sensed and the VRD control logic 370 commands the VRDswitch 350 to open, shutting down the input power side of the powersource 300.

When the VRD switch 350 is opened, because of a high output voltagecondition, and the on/off switch 340 is still closed, power is stillable to be supplied to the VRD power supply 360. As a result, thevarious components of the VRD device are still being supplied withelectrical power and are able to operate. In accordance with anembodiment of the present invention, to reset (i.e., close) the VRDswitch 350, the on/off switch 340 has to be toggled off and then onagain. This resets the VRD switch 350 and enables the input power sideof the power source 300, unless the VRD control logic 370 is stillsensing a no-load condition and a high output voltage condition, inwhich case the VRD switch 350 will immediately open again. Such asituation may indicate that the power source 300 requires servicing,repair, or replacement.

FIG. 4 illustrates a schematic block diagram of an example embodiment ofan improved voltage reduction device implemented in a second embodimentof a power source 400 of the electric arc welding system 900 of FIG. 1.The power source 400 of FIG. 4 is very similar to the power source 300of FIG. 3 except that the output power side of the power source 400 ofFIG. 4 is configured a little differently as a single phase full bridgeconfiguration. Instead of having a single secondary winding as in FIG.3, FIG. 4 shows a welding transformer 410 having two secondary windings412 and 413 and two SCR's 495 and 496. The output controller 399 isconfigured to enable and disable such a configuration of outputcomponents. The VRD components of FIG. 4 are the same as that of FIG. 3,however, and VRD capability and operation are the same.

FIG. 5 illustrates a schematic block diagram of an example embodiment ofan improved voltage reduction device implemented in a generic embodimentof a power source 500 of the electric arc welding system 900 of FIG. 1.FIG. 5 is intended to illustrate that the VRD device of FIG. 3 and FIG.4 may be implemented in many other types of power sources having variouspower converter configurations including single phase configurations andmulti-phase configurations (e.g., three-phase configurations) andinverter or chopper configurations, for example. FIG. 5 shows theauxiliary transformer 330 with the on/off switch 340, the VRD switch350, and the relay coil 321 in series with each other on the secondaryside of the auxiliary transformer 330, as in FIG. 3 and FIG. 4, fordisabling the input power side of the generic power source 500. FIG. 5also shows the output controller 399 for enabling and disabling theoutput power side of the generic power source 500. Again, the VRDcomponents of FIG. 5 are the same as that of FIG. 3 and FIG. 4, and VRDcapability and operation are the same.

FIG. 6 illustrates a schematic diagram of an example embodiment of avoltage reduction device (VRD) control logic 370 and associated logictruth table implemented in the voltage reduction devices of FIGS. 3-5.The VRD control logic 370 includes an AND gate 610 and an inverter 620.As seen in the logic truth table, when the load/no-load condition signal376 indicates a no-load condition (e.g., a logic “0”) and the high/lowcondition signal 373 indicates a high output voltage condition (e.g., alogic “1”), the signal 372 is a logic “1” and the VRD switch is opened(i.e., a logic “1” commands the VRD switch to open in this embodiment),disabling the welder input side of the power source. Furthermore, thesignal 371 to the output controller is a logic “0” which tells theoutput controller to disable the welder output side of the power source.As an example, a no-load condition may exist when the resistance betweenthe welding output terminals A and B is greater than 100 ohms.Similarly, a high output voltage condition may exist when the voltagebetween the welding output terminals A and B is greater than 50 voltsRMS (i.e., V_(T)>50 V_(RMS)).

Continuing with the logic truth table, when a no-load condition existsand a low output voltage condition exists, the welder input is enabledbut the welder output is disabled. When a load condition exists and alow output voltage condition exists, both the welder input and thewelder output are enabled. This may correspond to a situation where theelectrode E is being touched to the workpiece W forming a short. When aload condition exists and a high output voltage condition exists, boththe welder input and the welder output are enabled. This may correspondto an active welding situation, for example, where an arc exists betweenthe electrode E and the workpiece W.

Therefore, according to the logic of FIG. 6, the load/no-load conditionsignal 376 determines whether or not the welder output is enabled ordisabled. Both the load/no-load condition signal 376 and the high/lowvoltage condition signal 373 determine whether or not the welder inputis enabled or disabled via the VRD switch. Of course, in accordance withvarious embodiments of the present invention, the trigger switch signal377 and/or the current feedback signal 374 may be included in thecontrol logic as well (e.g., see U.S. Pat. No. 7,238,917).

FIG. 7 is a flowchart of an example embodiment of a method 700 forproviding voltage reduction capability in the electric arc welder 900 ofFIG. 1 using the voltage reduction devices of FIGS. 3-5 and the voltagereduction control logic 370 of FIG. 6. In step 710, the on/off switch340 is closed (and the VRD switch 350 is normally closed), enabling theinput power side of the welding power source. In step 720, if theresistive load on the output terminals A and B is less than a thresholdvalue R_(thres) (e.g., 100 ohms) indicating a load condition then, instep 730, the output power side of the welding power source is enabledand, in step 740, a user may proceed to weld.

If, however, in step 720, the resistive load on the output terminals Aand B is greater than the threshold value R_(thres) indicating a no-loadcondition then, in step 750, the output power side of the welding powersource is disabled. Furthermore, in step 760, if the output voltage(e.g., the RMS output voltage V_(RMS)) is not greater than a thresholdvalue V_(thres) indicating a low output voltage condition then, in step770, since the output power side is disabled and the output voltage islow, the welder is in a proper no-load safety condition.

However, in step 760, if the output voltage (e.g., the RMS outputvoltage V_(RMS)) is greater than the threshold value V_(thres)indicating a high output voltage condition then, in step 780, the inputpower side of the welding power source is also disabled. This providesan extra measure of safety in case a failure were to occur on the outputpower side of the welding power source, allowing power to get to theoutput terminals A and B (e.g., if the SCR 395 in FIG. 3 were to short).In step 790, the on/off switch 340 is reset (i.e., turned off and thenon again) in an attempt to reset the welder to re-enable the input powerside by causing the VRD switch 350 to close. The method 700 reverts backto step 760 to check if the high output voltage condition still exists.If so, the VRD switch 350 is immediately opened again.

In summary, an embodiment of the present invention comprises a method ofproviding a voltage reduction capability in a welding power source. Themethod includes sensing an induced signal, from within a welding powersource, to generate a sensed signal being indicative of a load conditionor a no-load condition between an electrode output terminal and aworkpiece output terminal of the welding power source. The methodfurther includes detecting an output voltage, from within the weldingpower source, being indicative of a low output voltage condition or ahigh output voltage condition across the electrode output terminal andthe workpiece output terminal. The method also includes disabling aninput power side of the welding power source, from within the weldingpower source, when the sensed signal is indicative of a no-loadcondition and the output voltage is indicative of a high output voltagecondition. In accordance with an embodiment of the present invention,the sensed signal is indicative of a no-load condition when a resistancebetween the output terminals is greater than about 100 ohms, and theoutput voltage is indicative of a high output voltage condition when theoutput voltage level is greater than about 50 V_(RMS). The method mayfurther include disabling an output power side of the welding powersource, from within the welding power source, when the sensed signal isindicative of a no-load condition. The induced signal is an oscillatingsignal induced in an output current path of the welding power source, inaccordance with an embodiment of the present invention, and the outputvoltage is a root-mean-square (RMS) voltage. The step of disabling theinput power side of the welding power source may be accomplished byautomatically opening a voltage reduction device (VRD) switch on theinput power side which is in series with a main ON/OFF switch of thewelding power source and a coil of an input power contact relay of thewelding power source.

Another embodiment of the present invention comprises a device forproviding a voltage reduction capability in a welding power source. Thedevice includes means for inducing an oscillating signal, from within awelding power source, in an output current path of the welding powersource. The device further includes means for sensing the inducedoscillating signal, from within the welding power source, to generate asensed signal being indicative of a load condition or a no-loadcondition between an electrode output terminal and a workpiece outputterminal of the welding power source. The device also includes means fordetecting an RMS output voltage, from within the welding power source,being indicative of a low output voltage condition or a high outputvoltage condition across the electrode output terminal and the workpieceoutput terminal. The sensed signal is indicative of a no-load conditionwhen a resistance level between the output terminals is greater than adefined threshold value, and the output voltage level is indicative of ahigh output voltage condition when the RMS output voltage is greaterthan a defined threshold value, in accordance with an embodiment of thepresent invention. The device further includes means for disabling aninput power side of the welding power source, from within the weldingpower source, when the sensed signal is indicative of a no-loadcondition and the RMS output voltage is indicative of a high outputvoltage condition. The device may also include means for enabling anoutput power side of the welding power source, from within the weldingpower source, when the sensed signal is indicative of a load condition.The device may further include means for supplying electrical power toat least the means for inducing, the means for sensing, and the meansfor disabling, even when an input power contact relay of the weldingpower source is not energized. The electrical power is derived from theinput power side of the welding power source through an auxiliarytransformer, in accordance with an embodiment of the present invention.

A further embodiment of the present invention comprises an apparatus forproviding a voltage reduction capability in a welding power source. Theapparatus includes a tuned receiver circuit configured within thewelding power source to receive an oscillating signal induced in thewelding output current path within the welding power source and togenerate a logical load condition signal therefrom. The apparatusfurther includes a voltage sensing circuit configured within the weldingpower source to detect a voltage between an electrode output terminaland a workpiece output terminal of the welding power source and togenerate a logical output voltage condition signal. The apparatus alsoincludes a voltage reduction device (VRD) switch in series with a mainON/OFF switch of the welding power source and a coil of an input powercontact relay of the welding power source on an input power side of thewelding power source. The apparatus further includes a voltage reductiondevice (VRD) control logic circuit configured within the welding powersource to open the VRD switch when the logical load condition signalindicates a no-load condition and the logical output voltage conditionsignal indicates a high output voltage condition. The apparatus may alsoinclude an oscillator circuit configured within the welding power sourceto induce the oscillating signal in the welding output current path. TheVRD control logic circuit may be further configured within the weldingpower source to command an output controller of the welding power sourceto enable an output power side of the welding power source when thelogical load condition signal indicates a load condition. The apparatusmay further include a VRD power supply configured to provide electricalpower to at least one of the tuned receiver circuit, the voltage sensingcircuit, the VRD control logic circuit, the oscillator circuit, and theVRD switch. In accordance with an embodiment of the present invention,the VRD power supply is operatively connected to an auxiliarytransformer of the welding power source on an input power side of thewelding power source. The VRD power supply is capable of derivingelectrical power from a secondary side of the auxiliary transformerwhether or not the input power contact relay is energized, and when themain ON/OFF switch of the welding power source is closed. The logicalload condition signal is indicative of a no-load condition when aresistance level between the output terminals is greater than a definedthreshold value. The logical output voltage condition signal isindicative of a high output voltage condition when the voltage isgreater than a defined threshold value.

While the claimed subject matter of the present application has beendescribed with reference to certain embodiments, it will be understoodby those skilled in the art that various changes may be made andequivalents may be substituted without departing from the scope of theclaimed subject matter. In addition, many modifications may be made toadapt a particular situation or material to the teachings of the claimedsubject matter without departing from its scope. Therefore, it isintended that the claimed subject matter not be limited to theparticular embodiment disclosed, but that the claimed subject matterwill include all embodiments falling within the scope of the appendedclaims.

What is claimed is:
 1. A method of providing a voltage reductioncapability in a welding power source, said method comprising: sensing aninduced signal, within a welding power source, to generate a sensedsignal being indicative of a load condition or a no-load conditionbetween an electrode output terminal and a workpiece output terminal ofsaid welding power source; detecting an output voltage, within saidwelding power source, being indicative of a low output voltage conditionor a high output voltage condition across said electrode output terminaland said workpiece output terminal; and disabling an input power side ofsaid welding power source, within said welding power source, when saidsensed signal is indicative of a no-load condition and said outputvoltage is indicative of a high output voltage condition.
 2. The methodof claim 1 further comprising disabling an output power side of saidwelding power source, within said welding power source, when said sensedsignal is indicative of a no-load condition.
 3. The method of claim 1wherein said induced signal is an oscillating signal induced in anoutput current path of said welding power source.
 4. The method of claim1 wherein said output voltage is an RMS voltage.
 5. The method of claim1 wherein said step of disabling said input power side of said weldingpower source is accomplished by automatically opening a VRD switch onsaid input power side that is in series with a main ON/OFF switch ofsaid welding power source and a coil of an input power contact relay ofsaid welding power source.
 6. The method of claim 1 wherein said sensedsignal is indicative of a no-load condition when a resistance betweensaid output terminals is greater than about 100 ohms.
 7. The method ofclaim 1 wherein said output voltage level is indicative of a high outputvoltage condition when said output voltage is greater than about 50V_(RMS).
 8. A device for providing a voltage reduction capability in awelding power source, said device comprising: means for inducing anoscillating signal, from within a welding power source, in an outputcurrent path of said welding power source; means for sensing saidinduced oscillating signal, from within said welding power source, togenerate a sensed signal being indicative of a load condition or ano-load condition between an electrode output terminal and a workpieceoutput terminal of said welding power source; means for detecting an RMSoutput voltage, from within said welding power source, being indicativeof a low output voltage condition or a high output voltage conditionacross said electrode output terminal and said workpiece outputterminal; and means for disabling an input power side of said weldingpower source, from within said welding power source, when said sensedsignal is indicative of a no-load condition and said RMS output voltageis indicative of a high output voltage condition.
 9. The device of claim8 further comprising means for enabling an output power side of saidwelding power source, from within said welding power source, when saidsensed signal is indicative of a load condition.
 10. The device of claim8 further comprising means for supplying electrical power to at leastsaid means for inducing, said means for sensing, and said means fordisabling, even when an input power contact relay of said welding powersource is not energized.
 11. The device of claim 8 further comprisingmeans for supplying electrical power to at least one of said means forinducing, said means for sensing, said means for detecting, and saidmeans for disabling, wherein said electrical power is derived from saidinput power side of said welding power source through an auxiliarytransformer.
 12. The device of claim 8 wherein said sensed signal isindicative of a no-load condition when a resistance level between saidoutput terminals is greater than a defined threshold value.
 13. Thedevice of claim 8 wherein said RMS output voltage is indicative of ahigh output voltage condition when said RMS output voltage is greaterthan a defined threshold value.
 14. An apparatus for providing a voltagereduction capability in a welding power source, said apparatuscomprising: a tuned receiver circuit configured within said weldingpower source to receive an oscillating signal induced in said weldingoutput current path within said welding power source and to generate alogical load condition signal therefrom; a voltage sensing circuitconfigured within said welding power source to detect a voltage betweenan electrode output terminal and a workpiece output terminal of saidwelding power source and to generate a logical output voltage conditionsignal; a voltage reduction device (VRD) switch in series with a mainON/OFF switch of said welding power source and a coil of an input powercontact relay of said welding power source on an input power side ofsaid welding power source; and a voltage reduction device (VRD) controllogic circuit configured within said welding power source to open saidVRD switch when said logical load condition signal indicates a no-loadcondition and said logical output voltage condition signal indicates ahigh output voltage condition.
 15. The apparatus of claim 14 furthercomprising an oscillator circuit configured within said welding powersource to induce said oscillating signal in said welding output currentpath.
 16. The apparatus of claim 14 wherein said VRD control logiccircuit is further configured within said welding power source tocommand an output controller of said welding power source to enable anoutput power side of said welding power source when said logical loadcondition signal indicates a load condition.
 17. The apparatus of claim15 further comprising a VRD power supply configured to provideelectrical power to at least one of said tuned receiver circuit, saidvoltage sensing circuit, said VRD control logic circuit, said oscillatorcircuit, and said VRD switch.
 18. The apparatus of claim 17 wherein saidVRD power supply is operatively connected to an auxiliary transformer ofsaid welding power source on an input power side of said welding powersource, and wherein said VRD power supply is capable of derivingelectrical power from a secondary side of said auxiliary transformerwhether or not said input power contact relay is energized, and whensaid main ON/OFF switch of said welding power source is closed.
 19. Theapparatus of claim 14 wherein said logical load condition signal isindicative of a no-load condition when a resistance level between saidoutput terminals is greater than a defined threshold value.
 20. Theapparatus of claim 14 wherein said logical output voltage conditionsignal is indicative of a high output voltage condition when saidvoltage is greater than a defined threshold value.